Containers made of corrugated paperboard have long been used for shipping and storing a variety of bulk materials such as powders, tobacco, metal castings, plastic resins, peanuts and many other materials. Such materials are often poured or thrown into the container and shipped loose so that the packed materials flow within the container. The side walls of the container must therefore be sufficiently rigid to withstand the internal movement of the load. Additionally, because it is often desired to stack one container directly on top of another for storage, the side walls must provide sufficient compression strength to prevent deformation or collapse of the container.
Various prior art containers have been provided in attempts to meet these requirements. Bulk pack containers have been provided with side walls formed of two and three layers of corrugated paperboard laminated together. Other containers have been provided having a multiple-cell construction or a center partition in an effort to decrease the internal movement of the bulk materials.
Even so, many problems still exist with these and other prior art containers. For example, in an effort to achieve the desired sidewall rigidity and compression strength, many prior art containers have been formed with a corrugated paperboard of increased weight and density. Yet, because all paper absorbs moisture, such containers lose their rigidity and compression strength when kept in a humid environment for an extended period of time. A warehouse typically provides just such an environment. As a result, these containers often deform and collapse, causing damage to the contents stored within. For the same reasons, multi-celled and partitioned containers have also proved ineffective.
Another prior art attempt has been to secure several layers of paperboard together using a moisture resistant adhesive. Because the paperboard is still subject to water absorption, such methods have proved only minimally effective. Additionally, the cost of these water resistant adhesives and the cost of applying these adhesives to the paperboard are extremely high.
Yet another prior art attempt to improve such containers requires manually inserting posts into the corners of the container. These posts are often formed of laminated paperboard, wood, metal or some other rigid material. While corner posts are very effective when used with a unit load container, they are ineffective when used with a bulk pack container. Because the bulk material will flow into the corners of the container, the act of inserting a post in the corner often causes damage to the bulk material. Furthermore, any movement of the packed material during shipment can dislodge the posts from the corners, rendering them useless as support members. Such movement of the bulk material can also break or splinter the corner posts, thereby contaminating the bulk material packed in the container. Yet another problem with corner posts in a bulk pack container is that by their very presence they decrease the amount of usable volume within the container. Furthermore, such hand placed posts increase the cost of manufacturing the container as a result of the additional labor required.
Thus, the prior art has heretofore lacked a bulk material container that provided the desired side wall rigidity and compression strength even under conditions of high humidity and heat.